1. Field of the Invention
The present invention relates to a heating apparatus for heating a material, such as, a semiconductor wafer, etc., to be heated to high temperature and, in particular, to an electron bombardment heating apparatus of the type in which accelerated electrons collide or impinge upon a heating plate, thereby generating heat thereon, and it relates to such an electron bombardment heating apparatus, in particular, which is superior in thermal stress-resistance, and also a temperature controlling apparatus and a control method of the electron bombardment heating apparatus, enabling both an increase of temperature with stability and a maintenance of a steady temperature.
2. Description of Prior Art
In processes for treating semiconductor wafers, etc., an electron bombardment heating apparatus of a type in which accelerated electrons are stroked or impinged upon the rear surface of a heating plate, thereby generating heat thereon, is widely used as a means for heating up a plate-like material, such as a semiconductor wafer, etc. In this electron bombardment heating apparatus, thermions generated through conduction of electricity into a filament are accelerated under a high voltage to impinge upon the rear surface of the heating plate, thereby generating heat in the heating plate and a plate-like material mounted on that heating plate is heated.
FIG. 6 attached herewith shows such an electron bombardment heating apparatus of the conventional art. In FIG. 6, though not shown in the figure, an upper portion of a stage portion 106 is located within an inside of a vacuum chamber and a portion of a heating plate 102 is located within a vacuum atmosphere.
In a wall of the stage portion 106, there is formed a coolant passage 107, and through this coolant passage 107 flows a coolant therein, such as water, etc., for example, thereby cooling the stage portion 106.
On this stage portion 106, there is provided a heat-resistive member 101 for supporting a material to be heated (hereinafter, being called by a “heated material supporting member”), having the flat heating plate 102 thereon, on which a thin plate-like material, such as a silicon wafer, for example, can be mounted to be heated, and within an inside thereof, there is defined a space hermetically separated from the outside thereof. In more detail, the heated material supporting member 101 is closed by means of the heating plate 102 on an upper surface side thereof, while being opened on a lower surface side, thereby having a cylinder-like shape. A lower end portion of the heated material supporting member 101 is fixed, abutting on an upper surface of the stage portion 106, and it is also hermetically sealed by means of a vacuum seal member 108.
As a material for making the heated material supporting member 101, for example, a heat-resistive silicon carbide impregnated with silicon, or a ceramic, such as, alumina (or aluminum oxide) or silicon nitride, etc. is used. In a case where the heated material supporting member 101 is made of an insulating material, such as silicon-impregnated silicon carbide, for example, an inner surface of the heating plate 102 is metallized for forming a conductive film thereon, and this conductive film is grounded through the stage portion 106.
On the stage portion 106 is formed an exhaust passage 104, and the space defined within an inside of the heated material supporting member 101 is evacuated by means of a vacuum pump 105 which is connected to the exhaust passage 104, thereby bringing about a vacuum condition therein.
Further, within the inside of the heated material supporting member 101, there are provided filaments 109. Those filaments 109 are located behind the heating plate 102 of the heated material supporting member 101 and, further, reflectors 103 are provided at the rear side of the filaments 109 for the purpose of heat blocking. To those filaments 109 mentioned above are connected a filament heating electric power source 110. Further, between those filaments 109 and the heating plate 102 is applied an acceleration voltage through the heated material supporting member 101 from an electron acceleration electric power source 111. However, the heating plate 102 is grounded and therefore is kept at a positive potential with respect to the filaments 109.
In an electron bombardment heating apparatus as was mentioned above, thermions are discharged from the filaments 109 when conducting electricity into the filaments 109 from the filament heating electric power source 110 and also applying the acceleration voltage of a certain high voltage between the filaments 109 and the heating plate 102 through the electron acceleration electric power source 111, and the thermions are accelerated under the acceleration voltage mentioned above, thereby impinging upon the lower surface of the heating plate 102. For this reason, the heating plate 102 is heated due to the electron bombardment.
When the temperature of the heating plate 102 rises, while measuring the temperature of the heating plate 102 due to the electromotive force generated in a thermocouple 112 by means of a thermometer 114, and when the temperature of the heating plate 102 reaches a predetermined value, the electric power supplied to the filaments 109 is lowered by an electric power adjustor 117, thereby maintaining the temperature of the heating plate 102 at the predetermined value. After passing a predetermined time period, the electricity is stopped to be conducted into the filaments 109, thereby stopping the heat generation of the heating plate 102, while cooling is started by means of the coolant flowing through the coolant passage formed in the stage portion 106, thereby lowering the temperature of the heating plate 102.
The heated material supporting member 101 is cooled on the lower end surface thereof, through a coolant, such as water, etc., flowing through the coolant passage 107 of the stage portion 106; e.g., via the stage portion 106. On the other hand, the heating plate 102 making up an upper wall of the heated material supporting member 101 is heated up, through the bombardment of the electrons, which are discharged from the filaments 109 and accelerated by means of the electron acceleration electric power source 111 of a high voltage. For this reason, a steep thermal gradient is established, in particular, between the heating plate 102 making up the upper wall of the heated material supporting member 101 and the lower end portion of the heated material supporting member 101 in contact with the stage portion 106.
However, the heated material supporting member 101 is made of, for example, a heat-resistive silicon carbide impregnated with silicon, or a ceramic, such as, alumina (or aluminum oxide), or silicon nitride, etc. and, therefore, is weak in thermal stress. For this reason, when starting the heating of the heating plate 102, only the heating plate 102 making up the upper wall of the heated material supporting member 101 shows thermal expansion. Accompanying this, the heated material supporting member 101 deforms and the thermal stress is concentrated, in particular, upon a shoulder portion defined between a peripheral wall portion and the heating plate 102. When repeating the heating and the cooling on the heating plate 102, the heated material supporting member 101 receives the thermal stress, repetitively and, therefore, there is brought about a problem that it fatigues and deteriorates, gradually, thereby resulting in the breakage thereof.